1. Field of the Invention
The present invention pertains to an activated carbon filter for removing toxic substances, e.g., dioxins and furans, from flue gases prior to entry into the smokestack.
In the search for further possibilities, which meet the requirements of the 17th German Federal Air Pollution Prevention Ordinance (17. BIMSchVO) and the Law on the Prevention and Disposal of Wastes (AbfG), an activated carbon filter was developed, in which the hydrocarbon-containing toxic substances re- formed due to cooling effects after the high-temperature combustion section --dioxins and furans--are completely removed from the flue gases after the precipitation of dust before discharge into the atmosphere.
It is now sufficiently known that mechanisms for the destruction of dioxins and furans exist in rotary tubular kilns because of the high oxygen concentration and temperature. However, it cannot be ruled out that due to deposition of these compounds on dust particles in the waste heat boiler and the flue gas cleaning equipment, or due to a new formation of the compounds, the flue gases will still contain these residual amounts of dioxins and furans when discharged into the atmosphere. In relation to the dust discharged from the furnace, the degrees of destruction are very high, but they are again reduced due to the new formation of these toxic substances behind the rotary tubular kiln.
The use of dry activated carbon filters for the final cleaning of the flue gases from refuse incinerator plants has been known from the literature and from practice.
German Offenlegungsschrift No. DE-OS 26,51,117 discloses a process for removing sulfur compounds, especially H.sub.2 S, from a synthesis gas, in which the mass transfer with the absorbent takes place mainly in the liquid phase, because the mass transfer takes place much more intensely and rapidly in the liquid phase.
It has been known from German Offenlegungsschrift No. DE-OS 38,41,889 that an activated carbon filter stage is installed in front of the clean gas smokestack after the gas cleaning stage of a refuse incinerator plant.
2. Summary and Objects of the Invention
The task of the present invention is to provide a device for removing toxic substances, e.g., dioxins and furans, from flue gases, e.g., in refuse incinerator plants, prior to entry into the clean gas smokestack, which satisfies the existing regulations of the 17. BIM Sch G and equivalent regulations, on the one hand, and with which particularly efficient and rapid mass transfer can be achieved, on the other hand. Complete adsorption of these isomeric hydrocarbons is to be achieved with this device, and the concentration of these toxic substances in the clean gas is to be reduced to below the detection limit.
According to the invention, an activated carbon filter is provided for removing toxic substances such as dioxins and furans, from flue gases prior to the flue gas entering into a smoke stack. The filter comprises a filter vessel with a filter cover or upper wall which is provided with a gas feed pipe and used for metered feeding of activated carbon and with means for metered feeding of water. At least one drainage device is provided in the filter vessel for removal of activated carbon sludge saturated with toxic substances. At an upper part of the filter vessel, at least one gas discharge pipe is provided and an overflow pipe is provided for drawing off saturated activated carbon-water mixture. Horizontal means defining a perforated partition is provided for forming a gas distributor above the outlet of the flue gas feedline. The means defining a perforated partition is preferably provided as a valve tray. The means defining a perforated partition may also be a lass filter with coarse pores. A rotatable mixing device is preferably provided arranged in the vessel bottom. This rotatable mixing device is preferably recessed in the vessel bottom via a sealing connection piece and is connected to a three phase drive. The rotatable mixing device is arranged adjacent the gas outlet of the gas feed pipe and a three-phase drive is fastened above or below the filter cover of the activated carbon filter. The gas feed pipe is preferably connected with a gas check valve arranged in the upper part of the gas feed pipe. Water is passed through the perforated partition via a pipeline into the lower part 15 of the filter vessel.
A control and regulating device is provided for metering activated carbon and water depending on the amount of flue gases to be treated. The control and regulating device also monitors the drawing off of activated carbon water mixtures saturated with toxic gas and dust particles through an overflow arranged in the side wall of the vessel and through a drainage device provided in the vessel bottom. The activated carbon filter may include a filter vessel or a plurality of parallel-connected filter vessels of square, polygonal, or circular cross section.
As a consequence of the rapid and efficient removal process that can be achieved with the activated carbon filter according to the present invention, the dimensions of the activated carbon filter can be kept small compared with filters according to the state of the art.
The device for carrying out the process according to the present invention can also be installed in existing refuse incinerator plants, e.g., after the flue gas scrubber in front of the blower of the clean gas smokestack.
In principle, the activated carbon filter according to the present invention can also be used for the final cleaning of flue gases in other incinerator plants, such as fluidized bed furnaces, low-temperature carbonization plants, etc.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.